MOLECULAR DYNAMICS SIMULATION OF SINGLE DROPLET EVAPORATION UNDER ALTERNATING ELECTRIC FIELD
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摘要: 利用分子动力学方法研究了正弦形式的交变电场对三维悬浮水滴在超临界氮气环境下蒸发特性的影响, 主要考虑了电场幅值和频率对液滴蒸发寿命和液滴瞬时蒸发速率的影响. 其中水滴由8000个水分子组成, 环境气体由27000个氮气分子组成. 首先利用分子动力学方法模拟计算了不同状态下水的物性参数以及亚临界条件下匀强电场对液滴蒸发特性的影响, 从而验证了分子模型和蒸发模型的正确性. 接着模拟了在不同幅值和频率的交变电场作用下水滴在氮气环境下的蒸发过程, 结果表明, 相比于无电场或匀强电场, 交变电场能够更显著地促进水滴的蒸发. 在频率一定时, 随着电场幅值的增大, 液滴的蒸发速率不断升高, 蒸发寿命不断下降, 且液滴的瞬时蒸发速率、液滴温度、水分子的排列结构等参数都会产生频率为所加电场二倍的振荡特性, 且电场幅值越大, 振荡幅值也越大. 而在电场幅值一定时, 随着频率的增大, 液滴蒸发寿命和速率并不是单调变化的, 而是在频率$f=5$GHz时, 分别达到一个极大值和极小值, 文中从液滴能量和分子排列结构两个方面解释了产生了这一现象的原因.Abstract: In this paper, the effect of sinusoidal alternating electric field on evaporation characteristics of three-dimensional suspended water droplet in supercritical nitrogen was studied by molecular dynamics method. And the effects of amplitude and frequency of alternating electric field on evaporation life and instantaneous evaporation rate of single droplet were mainly considered. The evaporation of droplet with 8000 water molecules in the environment of 27 000 nitrogen molecules was simulated and analyzed. Firstly, the physical parameters of water such as thermal conductivity at different temperatures and pressures were simulated using molecular dynamics method, and compared with the theoretical or experimental data. Then, the effect of uniform electric field on single droplet evaporation under subcritical conditions was studied, which was in good agreement with the results in literature, and verified the correctness of the molecular model and evaporation model. Lastly, the evaporation of single water droplet under the action of alternating electric field with different amplitudes and frequencies was simulated. The results showed that compared with the case of no electric field or uniform electric field, the alternating electric field could promote the evaporation of water droplet more significantly. When the electric field frequency was constant, with the increase of the electric field amplitude, the evaporation life of water droplet decreased gradually. Besides, the instantaneous evaporation rate, droplet temperature, and the arrangement structure of water molecules would produce oscillation characteristics with the frequency twice that of the applied electric field at a certain amplitude, and the larger the electric field amplitude, the greater the oscillation amplitude. However, when the electric field amplitude was constant, the evaporation life of droplet did not change monotonically with the increase of frequency, but reached a maximum and a minimum respectively at $f=5$GHz. The reasons for this phenomenon were explained from two aspects of water droplet energy and water molecular arrangement structure.
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Keywords:
- molecule dynamics /
- alternating electric field /
- droplet evaporation
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